Frost control in agricultural lands (e.g., orchards, vineyards etc.) is an important strategy for crop loss reduction. For example, where grapes, buds or vines within a vineyard die of frost, the income losses to an agricultural operation may be substantial, and accompanied by agricultural job losses. Frost control is particularly important in areas which are intensively cultivated, such as the California region of the United States of America. California accounts for one quarter of the food production for the USA, and half of its fruit and vegetables. Considering wine grapes solely in the Sonoma, Napa, Lake and Mendocino counties, even a 10% loss of production would cause losses of more than $80 million. Further, in California, it is estimated that in December 1990 alone, frost caused approximately $500 million in fruit loss and damages to about 450,000 hectares of tress.
A number of methods and technologies are used to provide frost protection in agricultural lands. One such method is to use sprinklers to water the plants and agricultural land during frost. The formation of ice is accompanied by the release of large amounts of heat, which maintains plants at freezing temperature as long as the water is being frozen. The continuous sprinkling of plants during frosty nights has been used to protect plants from frost injury. However, sprinklers consume large amounts of water, and the amount of water applied in the frost protection measures is hard to control.
Another method is to employ orchard heaters. Heaters, however, tend to pollute, are expensive and a relatively large number are needed to cover any significant area (e.g., about one every 100 feet). Hot houses may also be used to protect crops, but are very expensive, difficult to install and uninstall, and are very labor intensive. Helicopters have also been used to push warm air from above the inversion layer downwards, so as to counter frost. Helicopters are needless to say expensive to operate, noisy, consume gas and the application of this method may be time-consuming.
Wind machines are the most widely deployed method of frost protection (e.g., 70%-80% of Washington growers use wind machines), and provide relatively economical frost protection. Wind machines operate by employing a fan that mixes air within and above an orchard, field or vineyard so that the average temperature near the ground is raised.